The radar on NASA and JAXA's Tropical Rainfall Measuring Mission (TRMM) satellite saw Typhoon Usagi maintaining some of its inner-core structure an hour before landfall on Sept. 22, 2013. The data was used to create an image that showed the 3-D regions of heavy precipitation hiding under the circular cloud cover near Usagi's center of rotation.

While the light precipitation regions had lost the appearance of organization, the heavy precipitation regions showed what appeared to be a ~50 km/31.0 mile-radius eye wall, with multiple rain bands further away from the center. There is even some evidence that the compact inner eye wall, seen in previous overflights, had not completely disappeared one hour before landfall. The yellow arrow on the left side of the image shows the orientation of the viewpoint in the zoom view on the right side of the image.

The heavy precipitation was indicated there using the 40 dBZ radar reflectivity signal, and that signal barely reached a 6 km/3.7 miles altitude, indicating updrafts fell somewhat short of what would be required for lightning to form in the inner core. (dBZ means "decibels relative to Z" and is a meteorological measure of "Z," the equivalent reflectivity of a radar signal reflected off a remote object- which is the principle of Doppler Radar).

Consistent with this picture, the World Wide Lightning Location Network (WWLLN) saw no lighting in the inner core during an hour-long period centered on the time of the TRMM overflight. WWLLN did observe thunderstorm cells in the wake of the typhoon, several hundred kilometers/miles to the southeast over the South China Sea.

The counter-clockwise circling surface winds reached a peak of 94 knots/108.2 mph/174.1 kph at the city of Shanwei, China, approximately one hour after the TRMM satellite passed overhead in space. Early reports suggest Shanwei may have experienced the worst winds at landfall. This made Typhoon Usagi easily a category 2 on the Saffir-Simpson hurricane intensity scale. At the time of landfall in Shanwei, Hong Kong was only experiencing 25-30 knot/28.7 to 34.5 mph/46.3 to 55.5 kph winds, about 150 km/93.2 miles to the west of Shanwei. After making a surprise right turn during the final day before landfall, Typhon Usagi's center passed to the north of Hong Kong after landfall, bringing a maximum wind of 50 knots/57.5 mph/92.6 kph to various locations in Hong Kong between 2 to 6 hours after this TRMM overflight.

Southeastern China was hit by the most powerful typhoon of 2013 on Sept. 22, when Typhoon Usagi came ashore landfall in the Guangdong Province during the evening. NASA's TRMM satellite observed very heavy rainfall just south of the eye as the center was landfalling.

When Typhoon Usagi, the Japanese word for "rabbit," made landfall it had maximum sustained winds near 95.6 knots (~110 mph). According to Xinhuanet.com news, 25 people were killed by the storm. Over 310,000 residents were displaced due to the storm. Xinhuanet reported economic losses totaled as much as 7.1 billion yuan in Guangdong alone from Usagi.

On Sunday, Sept. 22, at 0900 UTC/5 a.m. EDT, Typhoon Usagi was closing in on the coast of southeastern China where it is poised to make landfall north of Hong Kong. Maximum sustained winds at that time were near 95 knots/109.3 mph/175.9 kph. At that time, the center of this large storm was near 22.6 north and 116.2 east, about 144 nautical miles/165.7 miles/266.7 km east of Hong Kong, but the effects of the storm were already being felt along the coast. Usagi was moving to west-northwest at 12 knots/13.8 mph/22.2 kph and generating very high, rough seas of up to 42 feet/12.8 meters. Coastal areas of southeastern China, and southwestern Taiwan experienced very rough surf as Usagi was making landfall.

Satellite data on Sept. 22 showed that Usagi's eye was about 10 nautical miles wide and beginning to cross the China coast. NASA's TRMM satellite passed overhead on Sept. 22 at 0923 UTC/5:23 a.m. EDT as the storm was making landfall, and TRMM saw very heavy rainfall in the southern quadrant of the storm. There were areas just south of Usagi's eye where rain was falling at a rate of over 169mm/~6.7 inches per hour along China's coast. TRMM radar sliced through Usagi and found that heights of some thunderstorms were reaching only about 12 km /7.4 miles but were returning values of over 54dBZ to TRMM's Precipitation Radar (PR) instrument.

According to CNN early (Eastern Daylight Time) on Sunday, Sept. 22, more than 80,000 people evacuated from the Fujian Province while evacuations also occurred in the Guangdong and Zhejiang provinces.

Xinhuanet reported that about 8,490 houses collapsed and there was damage to about 50,800 hectares of cropland. As Usagi's remnants move over land the rugged terrain north of Hong Kong toward Guangzhou will cause it to dissipate within two days.

The most powerful typhoon of 2013 was passing between northern Philippines and southern Taiwan on Sept. 19. When NASA's Aqua satellite passed over Usagi, infrared data showed a large area of powerful thunderstorms and heavy rain surrounding the center while NASA's TRMM satellite measured that heavy rainfall from space.

Super-Typhoon Usagi is a monster storm that according the Joint Typhoon Warning Center is headed for a landfall near Hong Kong on Sept. 22 around 1200 UTC/8 a.m. EDT/8 p.m. local time Hong Kong.

Usagi formed in the open waters of the Philippine Sea about 1,000 km/~620 miles east of the Philippines on September 16, 2013. Usagi rapidly intensified and became a typhoon on Sept. 18 and a Super Typhoon on Sept. 19 when it had estimated maximum winds of close to 140 knots/~161 mph.

NASA's Tropical Rainfall Measuring Mission or TRMM satellite had an excellent view of Usagi September 19, 2013 at 1035 UTC/6:35 a.m. EDT/6:35 p.m. local time Hong Kong. At NASA's Goddard Space Flight Center in Greenbelt, Md. a precipitation analysis from TRMM's Microwave Imager (TMI) and Precipitation Radar (PR) instruments was overlaid on an enhanced infrared image from TRMM's Visible and InfraRed Scanner (VIRS). The most striking feature on the image was Usagi's small, clear eye. Rain was measured by TRMM's PR instrument falling at a rate of over 140mm/~5.5 inches per hour in the powerful storms within super typhoon Usagi's eye wall.

TRMM's Precipitation Radar or PR can provide 3-D vertical profiles of rain and snow from the surface up to a height of about 12 miles/20 kilometers. TRMM's 3-D view of the vertical structure near Usagi's eye found that the violent storms in Usagi's eye wall were consistently reaching heights of over 15 km/~9.3 miles. A few storms found in a feeder band spiraling into Usagi from the south were reaching even higher heights of over 16 km/~9.9 miles.

After the TRMM satellite captured rainfall, NASA's Aqua satellite passed over the Super-Typhoon. The Atmospheric Infrared Sounder or AIRS instrument that flies aboard NASA's Aqua satellite captured an infrared image at 17:29 UTC/1:29 p.m. EDT that also clearly showed a pinpoint eye. AIRS measured cloud-top temperatures to determine cloud heights, which also indicate strength. Cloud top temperatures were as cold as 210 kelvin/ -81.6F/-63.1C, indicating very high, very powerful thunderstorms with heavy rainfall potential. Strong thunderstorms with heavy rain were over northern Luzon, Philippines at the time of the image. Infrared data on Sept. 20 revealed that convection (rising air that forms the thunderstorms that make up the tropical cyclone) in the northern quadrant were decaying, or weakening.

Satellite data also showed that Usagi was undergoing eyewall replacement on Sept. 20, which is typical for very powerful typhoons or hurricanes.

There are warnings in effect in Taiwan, the northern Philippines and China. Typhoon Warnings are up for Taiwan, especially for southeastern and southwestern areas as Usagi is forecast to move south of the island. In the Philippines, warnings and watches were posted for the northern provinces of the Philippines that include flash flooding, heavy rain, landslides and storm surges.

In China, the China Meteorological Administration or CMA issued an orange alert. The CMA's website noted that Usagi is expected to move across Bashi Channel at noon (local time) on Sept. 20 then enter northeastern South China Sea to approach coastal Guangdong.

On Sept. 20 at 1500 UTC/11 a.m. EDT, Usagi's maximum sustained winds dropped to 130 knots/149 mph/241 kph. The center of the storm was located near 20.3 north and 123.2 east, about 324 nautical miles south-southeast of Taipei, Taiwan. Super-Typhoon Usagi is moving to the west-northwest at 9 knots/10.3 mph/16.6 kph.

The latest Joint Typhoon Warning Center forecast projects that Usagi will pass north of the Philippines in the next couple days and then pass very close to the southern tip of Taiwan on September 21. This path exposes southern Taiwan to the most dangerous part of the typhoon.

The radar on the Tropical Rainfall Measuring Mission (TRMM) satellite captured an image of Supertyphoon Usagi near the end of a 24-hour period in which Usagi intensified by 65 knots. This is more than twice the commonly used 30-knot threshold for defining rapid intensification.

The TRMM data was used to create a 3-D image. The data was collected at 1035 UTC/6:35 a.m. EDT on Thursday, September 19, 2013, when Usagi was at category 3 on the Saffir-Simpson hurricane intensity scale. A few hours later, Usagi completed its lightning-fast intensification to category 5, the highest category in the scale. While the center of this tropical cyclone is forecast to past just south of Taiwan in a few days, some forecasts have it striking Hong Kong a few days after that.

A number of the features of the TRMM radar observations are consistent with a well-organized storm with an efficient "heat engine." A tropical cyclone's heat engine extracts heat from the ocean's surface through wind-enhanced evaporation and converts a portion of that energy into kinetic energy of the destructive winds that circle under the eyewall of the storm. The eyewall is an arc or ring of string storms just outside the mostly cloud-free eye at the center of rotation of the tropical cyclone.

Radars almost always see eyewalls in strong tropical cyclones, but few tropical cyclones have such symmetric eyewalls as does Supertyphoon Usagi in the TRMM 3-D image. The 3-D image was multi-colored to show the volume of the light precipitation lifted to high altitudes, and heavy precipitation at the base of the eyewall (using a radar reflectivity threshold of 20 and 40 dBZ, respectively). Even the heavy precipitation at the base of the eyewall is fairly symmetric which is somewhat unusual.

Tropical cyclone eyewalls that are this symmetric are called "annular," and they have a tendency to maintain their intensity for longer periods than do tropical cyclones with more lopsided eyewalls (Knaff et al., 2003). At two locations in the eyewall, updrafts are strong enough to lift ice precipitation up and out of the troposphere, the layer of the atmosphere that usually confines the weather. Such tall storm cells are called "hot towers" and are associated with periods of tropical cyclone intensification.

Lightning flashes were detected by a group of ground-based sensors called the World-Wide Lightning Location Network (WWLLN, http://wwlln.org). The WWLLN does not measure the altitude of the lightning, so the flashes were depicted in TRMM data at a 5 km altitude, which is near the freezing level in tropical cyclones and near the top of the heavy precipitation detected by the TRMM radar.

Lightning requires strong updrafts to form, indicating locations where storm cells are releasing considerable energy into atmosphere. It is an active area of research, however, to pin down the exact relationship between bursts of eyewall lightning and current or future changes in tropical cyclone intensity (Thomas et al., 2010; DeMaria et al., 2012). The lightning plotted in the TRMM image was observed during a 20 minute period centered on the time of the TRMM overflight. The flash rate was about 1.5 flashes per minute during this period, and the flash rate held fairly steady during a full six hours centered on the time of the TRMM overflight.

TRMM data is provided by NASA and JAXA. WWLLN data courtesy of Dr. Robert Holzworth (http://wwlln.org). Next year, NASA and JAXA will launch the Global Precipitation Measurement (GPM) satellite which will have advanced capabilities beyond those of TRMM (http://pmm.nasa.gov).

What was a tropical storm rapidly intensified into Typhoon Usagi within 24 hours as it moves through the Northwestern Pacific Ocean. NASA satellite data revealed a 20-mile-wide eye and bands of thunderstorms spiraling into the center of the monster storm.

The MODIS instrument, or Moderate Resolution Imaging Spectroradiometer aboard NASA's Terra satellite captured an amazing image of Typhoon Usagi on Sept. 19 at 02:25 UTC moving near the Philippines. The image showed spiraling bands of thunderstorms wrapping into the well-developed center of circulation and a clear eye. The bands of thunderstorms extend almost 300 nautical miles/ 345.2 miles/555.6 km to the north and about 240 nautical miles/276.2 miles/444.5 km to the south.

In 24 hours, Usagi's maximum sustained winds increased by 65 knots/75 mph/120 kph! What's interesting is that a Category one hurricane itself has maximum sustained winds near 74 mph/119 kph, and Usagi strengthened more than a category one in 24 hours.

The Joint Typhoon Warning Center or JTWC forecast indicates that Usagi is not yet at its most powerful. Usagi is expected to continue intensifying to a peak of 140 knots/161 mph/259.3 kph over Sept. 19, and could exceed that speed, according to JTWC.

Over the next two days, Sept. 20 and 21, forecasters at the Joint Typhoon Warning Center expect Usagi to move west-northwest and pass just south of the southern tip of Taiwan before making landfall near Hong Kong on Sept. 22.

When NASA's Aqua satellite passed over Usagi on Sept. 18 at 04:40 UTC/12:40 a.m. EDT, the Moderate Resolution Imaging Spectroradiometer known better as "MODIS" took a picture of the northwestern Pacific Ocean storm. The image showed thick bands of powerful thunderstorms south of the center of circulation, and wrapping tightly around the center. Convective banding was also developing in other quadrants of the storm, indicating the storm was intensifying. At the time of the MODIS image Usagi was far to the east of the Philippines.

Usagi is in an area of warm sea surface temperatures near 29 to 30 Celsius/84.2 to 86 Fahrenheit, which is helping the storm strengthen. Tropical cyclones need sea surface temperatures of at least 26.6C/80F to maintain intensity, and warmer temperatures can help a storm strengthen through evaporation.

On Sept. 18 at 0900 UTC/5 a.m. EDT, Usagi's maximum sustained winds were near 55 knots/63 mph/102 kph. Forecasters at the Joint Typhoon Warning Center expect Usagi to strengthen into a typhoon over the next day. Usagi was centered near 17.3 north and 128.7 east, about 565 nautical miles south-southeast of Kadena Air Base, Japan. Usagi is moving to the west at 3 knots/3.4 mph/5.5 kph.

The storm is expected to move northwest and stay over open waters of the northwestern Pacific Ocean while passing between the northern Philippines and southern Taiwan.

Infrared data provides a look at cloud top temperatures in tropical cyclones and there were very cold cloud tops in the thunderstorms banding around the south of newborn Tropical Storm Usagi's Center.

On Sept. 16, low pressure System 99W strengthened into Tropical Depression 17W. The depression became Tropical Storm Usagi very late in the day.

The Atmospheric Infrared Sounder or AIRS instrument aboard NASA's Aqua satellite captured an infrared image of Tropical Storm Usagi on Sept. 16 at 16:59 UTC/12:59 a.m. EDT. The image showed the highest storms and coldest cloud top temperatures around and south of the center of circulation. The cloud top temperatures exceeded -63F/-52C in those areas, indicating high thunderstorms, with the potential for heavy rainfall.

The Joint Typhoon Warning Center or JTWC is the forecast organization for this tropical storm. JTWC noted that animated infrared satellite imagery revealed the low-level circulation center was consolidating, although partially exposed to outside winds. The circulation center has become more tightly wrapped and a central dense overcast feature has started to build along the southern edge of the center.

When NASA's Tropical Rainfall Measuring Mission satellite called TRMM passed overhead on Sept. 17 at 1050 UTC/6:50 a.m. EDT, the TRMM Microwave Imager, or TMI showed that the low-level center was continuing to consolidate and wrap more tightly, while thunderstorms and convection continued to strengthen.

On Tuesday, Sept. 17 at 1500 UTC/11 a.m. EDT Usagi had maximum sustained winds near 40 knots//46 mph/74 kph. Usagi was centered near 17.6 north and 130.6 east, about 559 nautical miles/643 miles/1,035 km south-southeast of Kadena Air Base. Usagi was moving to the west at 5 knots/5.7 mph/9.2 kph.

The Joint Typhoon Warning Center forecast takes Usagi west toward the northern Philippines but turning to the northwest before reaching the country, and heading toward Taiwan.

TRMM satellite data provided a look at Typhoon Usagi's inner-core structure an hour before landfall on Sept. 22, 2013. Heavy precipitation (in deep red) was found near the storm's center.

Image Credit:

NASA Goddard Space Flight Center/Owen Kelley

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The AIRS instrument aboard NASA's Aqua satellite captured this infrared image of Tropical Storm Usagi on Sept. 16 at 16:59 UTC/12:59 a.m. EDT. The image showed the highest storms and coldest cloud top temperatures (purple) around and south of the center.

This TRMM 3-D image of Super-Typhoon Usagi on Sept. 19 shows heavy rain (red) at the base of the eyewall. The lightning flashes (ring of small orange dots) are displayed at 5 km altitude. That's near the freezing level in tropical cyclones and near the top of the heavy precipitation.

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NASA/Owen Kelley

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On Sept. 19 NASA's TRMM satellite saw rain falling at a rate of over 140mm/~5.5 inches (red) per hour in the powerful storms within Super Typhoon Usagi's eye wall.

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In this TRMM satellite flyover animation from Sept. 19 rain was falling at a rate of over 140mm/~5.5 inches (red) per hour in the powerful storms within Super Typhoon Usagi's eye wall.

On Sept. 22 at 0923 UTC/5:23 a.m. EDT, just south of Usagi's eye where rain was falling at a rate of over 169mm/~6.7 inches per hour along China's coast. TRMM radar sliced through Usagi and found that heights of some thunderstorms were reaching only about 12 km /7.4 miles.

Image Credit:

NASA/SSAI, Hal Pierce

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On Saturday, Sept. 21, TRMM captured rainfall data on Typhoon Usagi as it passed between the northern Philippines and southern Taiwan. TRMM found rain falling at a rate of over 134 mm/hr (~5.2 inches) in USAGI's eye wall.

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SSAI/NASA, Hal Pierce

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This simulated 3-D flyby animation over Typhoon Usagi on Sept. 22 at 0923 UT showed heavy rain south of the center a rate of over 169mm/~6.7 inches per hour along China's coast. Cloud heights of some thunderstorms were reaching only about 12 km /7.4 miles.